XDR Users are retrieved from the CSPortal (support.paloaltonetworks.com) -> Members -> Manage Users.
Note that you will have to delete the account from your CSP in order for it to be removed (not shown at all) from XDR/Users screen, if this is not desirable, this article can help:
Click Accept as Solution to acknowledge that the answer to your question has been provided.
The button appears next to the replies on topics you’ve started. The member who gave the solution and all future visitors to this topic will appreciate it!
These simple actions take just seconds of your time, but go a long way in showing appreciation for community members and the LIVEcommunity as a whole!
The LIVEcommunity thanks you for your participation!